A bush of a bearing, especially of a dry bearing, has a cylindrical body, and the inner surface of the bush serves as a bearing surface having an excellent sliding-contact property. The bush is fixed in a housing, and rotatably supports a rotary shaft inserted in the bush.
The rotary shaft supported by the bush has a diameter slightly smaller than an inner diameter of the bush and a clearance exists between the rotary shaft and the bearing surface of the bush such that the rotary shaft rotates smoothly. Consequently, the axis of the rotary shaft is vibrated, and errors occur in tooth engagement-contact and belt contact of gears and pulleys provided on end portions of the rotary shaft, thereby making it impossible to increase the mechanical accuracy. Moreover, the vibration causes other phenomena, for example, the rotary shaft collides with the inner surface of the bush and produces rattling noises.
A conventional technique known for preventing such an axis vibration is disclosed in JP-U-55-40249. In the conventional technique, as shown in FIG. 8, a bush 60 has a composite structure comprising an inner cylinder 61 made of resin and an outer cylinder 62 made of rubber provided on the outer periphery of the inner cylinder 61. Owing to a tightening force through the outer cylinder 62, the inner cylinder 61 is press-fitted on a rotary shaft S without forming a clearance therebetween, thus preventing vibration of the rotary shaft S. Also, even if the axis vibration occurs, vibration is absorbed by the buffer function of the outer cylinder 62, so that noises are not produced.
However, since the conventional bush 60 has the composite structure with the outer cylinder 62 provided on the inner cylinder 61, the structure is complicated, and also, the diameter of the bush 60 is increased by the thickness of the outer cylinder 62.